In recent years, the greenhouse effect, due to CO2 is pointed out as a factor of global warming, and thus the measure to cope with this has become an international urgent task in order to protect the global environment. The CO2 generation sources include a various fields of human activities that burn fossil fuels, and a demand for emission limitation of CO2 tends to be even stronger. In association with this, a method to remove and recover CO2 in the flue gas by bringing the flue gas from a boiler into contact with an amine-based CO2 absorbent, such as an aqueous alkanolamine solution or a method to store the recovered CO2 without releasing it to the atmosphere has been extensively investigated by taking the power generation facilities such as thermal power plants that use great amounts of fossil fuels as the target.
Hitherto, a method to remove CO2 (carbon dioxide) and SOx (sulfur oxides) in the flue gas is disclosed in Patent Literature 1. This method includes a denitrifying step of conducting the denitrification treatment by reducing NOx (nitrogen oxides) contained in the flue gas, a desulfurizing step of conducting the desulfurization treatment by bringing SOx contained in the flue gas into contact with calcium carbonate in the slurry, a CO2 removing step of absorbing CO2 in the flue gas to an absorbent by bringing the flue gas which has been subjected to the denitrification treatment and the desulfurization treatment into countercurrent contact with an amine-based absorbent (aqueous alkanolamine solution) in the absorber, and an absorbent regenerating step of obtaining a lean solution obtained by removing CO2 from the rich solution having CO2 absorbed in the regenerator and returning the solution to the absorber again. Moreover, in this method, reclaiming in which the absorbent is heated by a reclaimer to concentrate the coexist substance as sludge and the degraded substance is removed from the absorbent is conducted in order to prevent a situation in which degraded substances including a thermally stable salt produced through the oxidation degradation of the alkanolamine by the oxygen in the flue gas or the reaction of the alkanolamine with the remaining NOx or the remaining SOx and a solid such as smoke dust contained in the flue gas are accumulated in the system through which the absorbent passes.